In recent years, from a perspective of preserving the environment, it is becoming popular to use a wind turbine generator generating power from wind power. In a wind turbine generator, generally, a nacelle is supported by an upper part of a tower and a blade mounted to a hub is supported rotatably by the nacelle. In such wind turbine generator, motion energy of the wind is converted into the rotation energy of the blade (specifically, the entire rotor including the blade) and the rotation energy of the rotor is converted into electric power by the generator.
The wind turbine blade used for the above wind turbine generator, is desired to be lightweight to be supported at the top of the tower and is desired to have high strength to be subjected to the wind. This, fiber-reinforced plastic is often used for the parts constituting the wind turbine blade. The wind turbine blade conventionally includes, for instance, an outer shell formed of reinforced-fiber plastic, spar caps (a main reinforcement member) arranged on a suction side and a pressure side of the outer shell, and a shear web (a spar member) arranged between the spar caps.
As a conventional wind turbine blade, disposed in Patent Literature 1 is a wind turbine blade having a reinforcement member extending in a longitudinal direction of the blade and a shear web. The reinforcement member of the wind turbine blade is constituted of a part formed of carbon-fiber plastic and a part formed of glass-fiber plastic in the longitudinal direction. For instance, the part formed of glass-fiber plastic is arranged on a root side of the blade and the part formed of carbon-fiber plastic is arranged on a tip side of the blade (see FIG. 3). Generally, carbon-fiber plastic has higher strength than glass-fiber plastic. By using two different types of plastic materials for the reinforcement member as described above, the blade can be configured with high strength at low cost.
In Patent Literature 2, the wind turbine blade includes a part of the outer shell on the blade tip side is formed of a first fiber-containing polymer and a part of the outer shell on the blade root side is formed of a second fiber-containing polymer (see FIG. 2). For instance, a combination of the first fiber-containing polymer and the second fiber-containing polymer may be a combination of carbon-fiber plastic and glass-fiber plastic. To obtain enough strength in a transition zone between different materials, boundary surfaces where the carbon-fiber plastic is replaced by glass-fiber plastic may be displaced in relation to the other faces in a blade-cross-section (see FIG. 5).
As described above, the wind turbine blade is desired to be lightweight and have high strength. In addition to those, the wind turbine blade is desired to have lightning protection as the wind turbine blade is arranged at a high place on top of the tower and is easily subjected to lightning. In view of this, Patent Literature 3 proposes a lightning protection device having a lightning receptor on a surface of the wind turbine blade. The lightning protection device grounds lightning current via a connection device such as a conductive wire.